[Michael G.]

... Don't know how many T amp users already know this, but recently I have discovered (via email conversations with Michael Mardis, www.michael.mardis.com) that using the Sonic Impact T amp with headphones is probably a bad idea. Why does he strongly advise against using the T amp with the K-1000, or with any other headphones? Number one reason is that the little T amp puts out a LOT of DC offset. He's measured it to be about 100 mV of DC offset, which works out to be 8.3 mW into the AKG. Definitely not good for the little drivers on the AKG over the long term! Also, the ultrasonic noise filters on the T amp were not designed to work properly outside of a 4 - 8 ohm load. Into the high-impedance load typical of most headphones, this problem will manifest itself as audible background hiss because the T amp puts out a lot of RF. While the RF noise problem can be addressed by connecting 6 ohm resistors in parallel with each of the speaker terminal outputs, the only way to tackle the DC offset problem would be to install something like a DC null circuit. If you are using the T amp to drive your AKG's it might be a wise idea to stop doing so, at least until you have somehow installed a large DC blocking capacitor in the output stage of the amp... Sheesh! For those of us who thought we had found an inexpensive way to drive the K-1000's satisfactorily, this is disappointing news indeed. Will the search for a good, affordable amp for these headphones ever end?

 

[Tachikoma]

What about the other tripath chips (TA2020, TA2022)?

 

[Michael G.]

No, I don't not know if these problems are characteristic of any other "T" class amps.

 

[Tachikoma]

Quote:

Headphones on the Sonic DON'T DO IT! Here's why. 1) The Sonic is a bridged amp. The negative output terminals CAN NOT be connected together. You would have to rewire your headphones to dual mono to use a bridged amp. 2) This is a switching amp. The Tripath amps work by switching the output transistors fully on and off at a high frequency. Any shift in the switching pattern results in low frequency artifacts, i.e. - "audio". The high frequency swithing power must be filtered out to extract the audio. The filter is not perfect, so some ultrasonic noise remains. Not enough to bother normal speakers, but not good to put into your headphones. Which brings us to point: 2B) Filters. The output filters on the Sonic Impact are designed to work with 4-8 ohm drivers. Headphones typically have a much higher impedance, so the filter will not work in the range it was designed for. Thus even more ultrasonic noise in your headphones and your eardrums. 3) DC offset: The Tripath amps have a bit of DC offset. On the Sonic can run quite high, much too high for headphones. You would need a large DC blocking cap between the amp and the headphones 4) As great as this amp sounds on speakers, it doesn't sound very good on headphones. You would be much better off with one of the nice opamp or even tube driven headphone amps. How do I know? I test my amps with headphones. But I have a special rig to eliminate much of the ultrasound and all the DC offset. NO, I will not tell what it is. See below. 5) If you do use this amp to drive your headphones, be warned! Your head may explode! And I will not come over to clean the walls and the carpet. If you are foolish enough to use headphones with this amp, please mention me in your will.

I'm pretty sure that there are lots of people using the K1000 with the T-amp, at the moment, so I wonder why we haven't heard of anyone blowing up their heads from doing that yet XD

What I really want to know is, do the same problems still apply if you use a T-amp with one of the old stax energizers (SRD series)? Will the energizer block out the DC offset?

 

[Michael G.]

Quote:

Originally Posted by Tachikoma I'm pretty sure that there are lots of people using the K1000 with the T-amp, at the moment, so I wonder why we haven't heard of anyone blowing up their heads from doing that yet XD What I really want to know is, do the same problems still apply if you use a T-amp with one of the old stax energizers (SRD series)? Will the energizer block out the DC offset?

True, some people have used (and still do use) the T amp with the K-1000. Michael Mardis is being little facetious with that statement, but the point is that if you try to use the T amp with headphones you will be treated to a fair amount of background hiss and and a little too much DC offset. I recently tried a (modded) T amp with my K-1000's, and I did hear a fair amount of background hiss - until the amp stopped working altogether after about 1 minute of playback... Looking back, I'm glad the amp took a nosedive because I may have eventually damaged the expensive AKG drivers running that little thing on for hours. But, I must say that prior to the amp's untimely self-destruction, the music did sound quite vivid and clear... Don't know a thing about the Stax unit, however.

 

[jjcha]

Quote:

Originally Posted by Michael G. Michael Mardis is being little facetious with that statement, but the point is that if you try to use the T amp with headphones you will be treated to a fair amount of background hiss and and a little too much DC offset. I recently tried a (modded) T amp with my K-1000's, and I did hear a fair amount of background hiss -

Hmm, this is interesting. Honestly, I'm a little puzzled by this, as a fair number of seasoned ears and K 1000 users have heard my K 1000 and modified T-Amp, and none of us have ever detected a background hiss on it. Not to say this isn't an issue - just I've been using mine pretty regularly for a while now and it works fine.

Sonically, I don't think it brings out quite what I want with the K 1000, but right now I'm kind of focused on other rigs...

Best,

-Jason

 

[xand1x]

Well if this becomes a SERIOUS issue with people, which doubt it will, I hope a solution will be readily available for consumers. I mean, the t-amp has a great price to performance ratio..sucks to hear that RF and DC offset output levels make it dangerous for headphones! Although most haven't had problems, yet, so hopefully it doesn't become too much of an issue (head-fier's wallets are watered down enough as is

)

 

[Jahn]

I've heard the T-amp with the K1000 from my Tushi, and there wasn't any background noise at all. Dave Brubeck sounded just groovy.

 

[Michael G.]

Quote:

Originally Posted by jjcha Hmm, this is interesting. Honestly, I'm a little puzzled by this, as a fair number of seasoned ears and K 1000 users have heard my K 1000 and modified T-Amp, and none of us have ever detected a background hiss on it. Not to say this isn't an issue - just I've been using mine pretty regularly for a while now and it works fine. Sonically, I don't think it brings out quite what I want with the K 1000, but right now I'm kind of focused on other rigs... Best, -Jason

It's not that I don't believe you. But when I contacted Vinnie Rossi (of Red Wine/Clari-T fame), he seemed to know about the potential for noise problems when the T amp is used with headphones. He suggested to me that I install 6 ohm resistors on the speaker outs. Is it possible that your "modded" amp has also had resistors installed to help quench the RF noise? Or, could it be that the background noise I heard from my T amp was due to the fact it was ready to die? I know that there have been a lot of quality-control problems with Sonic Impact products so maybe that is the cause of some of these complaints? I never tried another T amp after my first experience, having been scared off. Interestingly, Michael Mardis never claims to have used the T amp with K-1000's. He does claim that he heard "horrible" levels of background noise when he tried to drive his Grados and some other phones with the T amp. I'm open to the suggestion that only certain defective units have the noise problem, but the DC offset issue still concerns me.